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Can gliding your plane save fuel?
Aimed towards lighter piston planes including a powered glider, if a pilot wants to extend a plane's range unconventionally, could flying like a glider by climbing and then gliding down or would flying straight, lower or slower save fuel; even if it means extending flight time?

This is the sort of question that can be answered right away by the fact that nobody ever does it.

Please note that some air-cooled piston engines can be damaged by cooling too fast. So if you switch them off, and then glide (or dive) for an extensive time period, they might cool down too fast.

To approach this with some napkin math / intuition...
In general, you want to maximize time gliding and minimizing time climbing, as that'd minimize fuel burn. Lets say you had a O-320 that burned 12gph in climb at max power. And for your plane Vy was 75kts w/ 500fpm climb rate and a 100kt cruise was 8gph, and coincidentally best glide was 75kts w/ a 800fpm descent rate. These are ballpark of a Cherokee/Skyhawk...
If you climbed 12min at 500fpm you'd end up gliding 7.5min, because 500fpm/800fpm = 0.625 and 0.625*12min = 7.5min.
Your total time for climb+glide would be 22.5min.
Using a total fuel of 12gph * 0.2hr = 2.4gal fuel burn from the climb.
You'd cover 28.125NM = 22.5min/60min/hr * 75kts.
Giving a fuel economy of 28.125NM/2.4gal = 11.72NM/gal.
In comparison, in normal cruise you'd be doing 100kts/8gal/hr = 12.5NM/gal
If this planes best glide descent rate magically became 500fpm (same as the climb rate) then you'd get a 12.5NM/gal economy when using climb+glide. This convenience is only because best glide speed equals best climb speed, which are usually relatively close on many GA planes. Naturally, for powered gliders their glide performance is much better than their climb performance so the climb glide method would be more efficient + more range.
Although, gliding may not be the best choice for every plane? To really solve this you'd need to do a system of equations defining the physics of aircraft performance...
To solve this you'd need:

the plane's drag polar, how much drag do I make?
relationship of propeller efficiency to advance ratio, how much power do I need to put into the prop to make thrust = drag?
relationship of engine's BSFC to RPM, how much fuel does it take to make the required power for the prop?

The tricky thing here is keeping assumptions reasonable, the classic "garbage in, garbage out" challenge.
Tangent story:
Once when flying a tow-plane with a low-pitch fixed pitch prop, I did a similar climb/descend profile to get a faster average cruise speed. In level flight you could do only about 85kts before redlining the engine, yet you could still climb over 500fpm at full power at 85kts. So, I'd climb to 8000ft-ish then establish a partial-power 200fpm descent at +100kts to my destination. The end result wasn't much better, +10kts gain and certainly more fuel burn, but it made me feel better and was fun :)

You still following?

@Justintimeforfun Not directly, I just saw a notification when checking stackoverflow. Did you need to ask something?

I didn't give a fly by user the accepted answer. Thanks!!

This approach of using an engine is called pulse and glide. It generally works because each engine has an optimal power setting at which it converts fuel into power most efficiently.
If the most efficient power is higher than is required, something should be done to accumulate and later use the excess energy. Raising the vehicle up looks like a solution, better than accelerating.
This method can only work if the power to efficiency curve of the machine is known. Otherwise, it is easy to do worse.

I guess the extreme case would be, in an existing plane, to optimize the propeller for climb. Purely guessing, but I think most self launching sailplanes (motorgliders) are designed with this climb only optimization as target.

Here is one thing that WILL save fuel-- where possible-- such as when flying VFR.
Note that this strategy only applies within the layer where thermal convection or orographic uplift are significant, not at higher altitudes where the air is generally not rising or sinking to any significant degree (apart from wave lift in which case the strategy will still apply!).
Don't try to hold a constant altitude on the second-to-second or minute-to-minute timescale.  Instead, hold a constant airspeed, while leaving your power setting fixed.  If your plane is climbing in an updraft, let it.  If your plane is descending in a downdraft, let it.  Then on a longer timescale-- maybe every few minutes or 5 minutes-- make a power adjustment (or airspeed adjustment) until you find the power / airspeed combination that gives an AVERAGE sink rate of zero over the long run.
The point being that if you make elevator inputs as needed to hold a constant altitude as you fly through updrafts and downdrafts, while operating on the front side of the power curve as we generally do, you end up speeding up in "lift" (updrafts) and slowing down in "sink" (downdrafts), which tends to maximize your time spend in downdrafts and minimize your time spent in updrafts -- the exact opposite of what a glider pilot would do to maximize efficiency.  So for a given total fuel burn over a given range, your average airspeed will actually end up being lower when you fly the conventional way, i.e. when you maintain a constant altitude.  Or for a given average airspeed, your fuel efficiency will be lower when you fly the conventional away.
You can take this idea one step further by slowing down a few knots in updrafts and speeding up a few knots in downdrafts-- providing that you don't take it to such an extent that it interferes with your ability to detect whether the air is rising or sinking, i.e. that the resulting changes in vertical speed don't dwarf the changes in vertical speed caused by the atmospheric movements.
Now, as for your idea of a powered climb followed by a (power-off) glide-- if you can feather the prop, there might be some benefit to this strategy, especially if you shut the engine down completely during the glides.  As long as the engine is running, you might as well get the most out of it by producing enough power to climb.

Your question should emphasize "still air" conditions and not get into exploiting vertical air motion, which is a separate issue completely.
For normal airplanes, the basic issue is, you want to spend the enroute phase of the flight at the end of an optimal climb profile, with an optimal cruising altitude (which will depend on winds) for as long as possible, with a Top of Descent that starts at the perfect location to complete a power off glide to the runway. This is what airliners and pretty well everybody else does, or strives for.
Gliding and climbing takes you away from an extended time at optimal altitude and power settings and replaces them with intermittent climbs at non-optimal power settings and altitudes, with the glides in between. The total energy needed to complete the flight will be higher, for the same overall profile.
Bottom line is, if there was any efficiency benefit to doing that sort of thing, somebody somewhere would be doing it, and absolutely nobody does.

-1: this is not true for all aircraft. It is well-known that "saw-tooth" flying is optimal for motor-gliders.

By this logic there would be people driving 55 mph on the freeway. Time is valued over efficiency (at least until carbon emissions are properly taxed).

@johnDanger air transport is not freeway driving and both the time and the fuel cost money and are accounted for in the cost index. Notably, in recent years, depending on the fuel prices, there is more and more weight given to the fuel consumption, compared with the past decades, and indeed a (somewhat) slower speed is often chosen.

@Vladimir F Time is valued with efficiency is more what I meant. Everyone isn't driving 80 mph (even when it is allowed) either.

@MartinArgerami a glider with a retractable engine who's drag is completely eliminated in the glide is "cheating" and doesn't count here.  We are talking about normal airplanes.

@JohnK: "powered glider" is mentioned explicitly in the first line of the question, so it's definitely "normal" in the context of this question. And if you are talking about a restricted category of aircraft, you'll have to rewrite your third paragraph where you speak as if what you say is a general principle.

I added an edit.  Still however, sawtoothing is something feasible on 45:1 gliders with retractable engines, not so much a 25:1 motorglider that has, maybe, a feathering prop, where at best it's a draw between one method or the other.

My recollection from a long time ago (say, when the Grob 109 was new) was that saw-tooth applied to it also as the most efficient cruising techinique; but I might be wrong there.

Remember when Major Gant (Clint Eastwood) stole one of the Firefoxes and was running out of fuel? There was a climb, a glide, and a dramatic landing on the ice floe (it was a movie). Was that the best way?
Perhaps so. One might imagine (for greatest distance), climbing at Vy, then gliding at Vbg. There would be some TAS benefit by getting as high as possible as well. This will also give you more options as to where to glide should gliding become necessary.
For lighter piston planes, with fixed pitch props, one can consult the POH to get fuel burn rate per hour and literally calculate best miles per gallon at a given power setting. So, one might try a Vy climb at optimal fuel burn RPM, if it is better than full open throttle (lower RPMs would allow a leaner fuel/air mixture).
But you can save fuel by getting best climb performance at Vy and best glide performance at Vbg.
Good trip planning should provide alternate landing sites to avoid this scenario, and, particularly when flying into a head wind, the field you passed may be your best choice to land.

Wait, you're using movie physics to validate a real-life claim? Have you ever heard of Mythbusters?

Clever, but it's obviously not validating, but illustrating.

Keep in mind that no mechanical, power producing system can operate with 100% lossless efficiency. In heat engines, like those in aircraft, the Carnot model describes the theoretical maximum efficiency (power produced vs lost) in any given design. Another way of asking your question would be, "Can I save fuel by taking my foot off the accelerator in my car?" Perhaps, the answer could be "Yes" of you utilize the environment to introduce power back into the system - like allowing gravity to accelerate you down a hill. But ultimately, the net power lost would have to be less than in Vbe cruise flight.
The problem is, if you must constantly regain altitude lost from gliding , you will have a net loss in energy when you climb to regain it again. IF (that's a big 'if') you were in a light enough plane AND (that's a big 'and') you were able to introduce supplemental energy into the system from somewhere besides the engine, like rising in thermal updrafts, you might save fuel by doing this, but at that point, you're just flying a glider (and one that is poorly equipped to fly in that way).
Every meter of progress toward your destination is paid for by energy. At Vbe, you know you are getting the best price per meter out of your engine. Any meter flown above or below this speed means you are overpaying, unless it is offset by free energy from the environment - gravity, updrafts, tailwinds, etc. Rather than tallying over-expenditures vs situational energy gains - hoping for a net improvement, which would require a delicate balance of variables, many of which are out of your control and difficult to predict, the surest way to achieve maximum fuel efficiency for distance is to cruise at Vbe.

The car analogy does not apply. You can certainly save fuel in a car by taking your foot off the accelerator in order to avoid putting your foot on the brake But since the vertical motion of the car can not be changed (except by taking a different road from A to B!) this is fundamentally different from the situation with a plane.

@alephzero: The analogy is meant to illustrate that, in certain circumstances, someone can allow the natural environment to contribute energy into the system. I think the confusion is coming from the fact that I use that analogy right before talking about regaining altitude in a plane. Letting off of the gas on a downhill in the car is akin to riding updrafts in a plane. But, on a flat road, allowing the car to coast and slow, before speeding back up for your next coast is less efficient than holding the constant best fuel-efficiency speed. Maybe I can edit to make it more clear.

authors: Vladimir F Героям слава


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Is it feasible to add an aftermarket hydrofoil to a light aircraft?
Could long, aftermarket hydrofoils be added to the water-skids of a plane (like this Cessna with pontoons or smaller)

Cessna 208 Caravan
not designed to have a hydro foil, to increase its ability to land on choppier water?
In theory, the pilot would first enter the water with the skids, clear of the chop, then stall the hydro foil similar to stall landing a plane thus giving the plane a soft or possibly vertical landing.

Grumman JRF-5 with hydrofoils

The chances of getting the angle of attack wrong when it hits the water the first time seems like it would rule this out.

Would you please [edit] your post to include source attribution for your images.

@FreeMan It took me some time to find them off Google Images, but I'll try to find a website that has these planes.

It's been done.  David Thurston designed a system for the Lake LA-4 that was purported to allow it to land on 5ft waves.  It may have been a bit of a handful (the Buccaneer is a demanding airplane on its normal hull). It was crashed by someone who took it for a spin without Thurston's authorization, and that was the end of that.

Nice find on the plane. I'm looking for something or way to make the work for a much smaller and cheaper aircraft.

@Justintimeforfun: But where do you find a smaller & cheaper airplane that will float?

As soon as that hydrofoil touches the water you're going to get a significant pitch down from the moment arm, I can imagine that would make it challenging.

@GdD right, especially in a plane with such high center of mass. But I think this technology could be quite promising for electric planes, with batteries in the keel making it more stable. If we can even computer-control the hydrofoils' attitude, better yet.

So you want to add lots of weight on a long moment arm @leftaroundabout? How's that going to help stability?

@GdD -- because of the "pendulum effect".  See https://aviation.stackexchange.com/questions/53437/does-pendulum-effect-apply-to-hang-gliders-or-any-aircraft/56548#56548

@GdD I think the pendulum effect had been compensated with the Grumman JRF-5 with hydrofoils plural. The forward arms of the picture in the question seems to have an extra set of foils to prevent the nose from tipping forward into the water on landing. With hydrofoil technology being improved such as the wing I think there again there maybe a reason to explore this landing gear again for choppy water landing.

I would make a serious study of this man's work.
Rostislav Alexeyev's "day job" was the design of large hydrofoil ferries, such as the Raketa carrying over 60 people, in the 1950s. This (image from linked article) and its successors are probably the most successful series of hydrofoils in the world.

He went on to design a series of Ekranoplans, ground effect flying vehicles. (pictured, A-90 Orlyonok, from here

These, despite being designed at his Central Hydrofoil Design Bureau, all seem to have used conventional stepped hulls like flying boats or seaplane floats.
He is probably the best person to tell you why.

The most interesting fact are theses plane are more efficient than modern airliners and hydro foils could allow the a ground effect plane to clear swells in the ocean. It is that rouge wave that makes this dangerous in open seas.

The reason the Ekranoplan uses a conventional hull is pretty simple - a hydrofoil requires a bit of speed to get going and at that point it's already flying. A foil would just be dead weight.

@papirtiger true for a suitable definition of "a bit of speed" ... hydrofoils can lift a hull clear of the water at sailboat speeds ... like 5 knots https://www.youtube.com/watch?v=UokOO60dsMU

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What is a squall line and how it is created?
How are squall lines created and what are they exactly?
If we encounter them how we deal with them?
I know that it is a narrow band of thunderstorms that is moving, but is there any other weather phenomena associated with it or no?

Thunderstorms can be associated with frontal weather movements, or can just form randomly away from frontal action by local convective activity.
A squall line is an array of thunderstorms triggered by uplift related to frontal movements instead of just randomly forming in a large air mass, basically in a line that is parallel, and in advance of, the cold front.
So the bottom line is, away from frontal conditions with a humid air mass and lots of sun, you can expect thunderstorms to form more or less randomly within the warm airmass. But when there is frontal activity where a cold front is advancing, you can anticipate multiple thunderstorms to form on the warm side of the front like a big commercial broom; a squall line.
As far as staying out of trouble and for flight planning, it might be possible to get from A to B VFR, where there are random thunderstorms not associated with a cold front, if the visibility is good enough to see the storms from a safe distance and they can be bypassed while maintaining good VFR conditions and staying at least 20 miles from the edge of the storm.
To be safe you need to have plenty of reserve fuel for diversions, and be ready to head for the hills if things aren't looking good. A hazy day with only 5 miles visibility and random cells lurking? You won't find me out there without weather radar in the plane.
And if you're planning to go from A to B, and there is front moving across your path, with lots of humidity and instability on the warm side, and you need to get across it, you can expect squall lines and you will be sitting on the ground until the front has passed and your trip is fully within the cold side.
It's always a good idea to be totally terrified of thunderstorms, and act accordingly, because the terror is justified.

Squall lines are just as you say, bands of thunderstorms moving in the same general direction. They are formed by convective activity, that is the sun heating the earth, which heats moist air which rises high into the atmosphere to form clouds.
As for other weather phenomena, tornadoes are relatively common in some areas as is hail.
As for how you deal with them you avoid them in light aircraft as they are hazardous. Even without the tornadoes and hail squall lines have high winds, wind shear and turbulence. Airplanes with weather radar and anti-icing may be able to find a way through, although caution is still required.

Find their way through, or, preferably above or around.

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When is a runway considered to be wet or slippery for 135 or 121 landing performance considerations?
For the purposes of following FAA regulations, when is a runway considered to be wet or slippery in the context of landing performance calculations? Specifically, what definitions or guidance on meaning for the terms "wet" or "slippery" should a pilot or dispatcher use in making the determination required by §135.385 or §121.195 as to the runway condition?
14 CFR 135.385 gives the following regulation pertaining to §135 operations of Turbine powered Large Transport Category airplanes:

Large transport category airplanes: Turbine engine powered: Landing limitations: Destination airports.
(d) Unless, based on a showing of actual operating landing techniques on wet runways, a shorter landing distance (but never less than that required by paragraph (b) of this section) has been approved for a specific type and model airplane and included in the Airplane Flight Manual, no person may take off a turbojet airplane when the appropriate weather reports or forecasts, or any combination of them, indicate that the runways at the destination airport may be wet or slippery at the estimated time of arrival unless the effective runway length at the destination airport is at least 115 percent of the runway length required under paragraph (b) of this section.

Likewise, 14 CFR 121.195 gives the following regulation pertaining to §135 operations of Turbine powered Large Transport Category airplanes

Airplanes: Turbine engine powered: Landing limitations: Destination airports.
(d) Unless, based on a showing of actual operating landing techniques on wet runways, a shorter landing distance (but never less than that required by paragraph (b) of this section) has been approved for a specific type and model airplane and included in the Airplane Flight Manual, no person may takeoff a turbojet powered airplane when the appropriate weather reports and forecasts, or a combination thereof, indicate that the runways at the destination airport may be wet or slippery at the estimated time of arrival unless the effective runway length at the destination airport is at least 115 percent of the runway length required under paragraph (b) of this section.

These regulations are effectively identical.
How is this determined? Does the FAA offer a definition (I have not found any such definitions in 14 CFR)? Does an AC give the appropriate definitions? Is the Operator expected to make this determination or to include a definition in the accepted or approved GOM? Should pertinent aircraft manufacturer's data be considered, for example if the AFM includes a definition of "wet runway"?
I am especially asking for any cases where the AFM does not give approved wet or contaminated landing data. Note the difference between approved and advisory AFM data. However, I am interested in knowing any and all ways in which the determination required by these regulations is complied with.

Can you give an example of a situation in which you'd be unsure whether or not the runway counts as "wet or slippery"? The phrase seems pretty unambiguous to me.

@TerranSwett For example, certain Cessna Citation AFMs include an advisory definition applying to certain situations where "wet" is defined as when the runway surface appears reflective. This definition has no bearing whatsoever on the FAA regulations, but has gained a significant, if not widespread, hold in certain sectors of the pilot community as the applicable definition when determining whether a runway is wet in applying §135.385. Additionally, when the runway is "damp" but not "wet" according to other jurisdictions, the FAA does not provide such distinctions.

@ymb1 I don't like using the 'far' tags because they have not been the FARs for wire some time now. It is 14 CFR. I thought the '-operations' tag fit better since this is an operations question.

I also could not find a definition for wet or slippery by the FAA, only for a contaminated runway:

CONTAMINATED RUNWAY− A runway is considered contaminated whenever standing water, ice, snow, slush, frost in any form, heavy rubber, or other substances are present. A runway is contaminated with respect to rubber deposits or other friction-degrading substances when the average friction value for any 500-foot segment of the runway within the ALD fails below the recommended minimum friction level and the average friction value in the adjacent 500-foot segments falls below the maintenance planning friction level.

(FAR/AIM Pilot/Controller Glossary, emphasis mine)
My Boeing 737 FCTM does however define:

A slippery surface is any surface where the braking capability is less than
that on a dry surface. Therefore, a surface is considered “slippery” when it
is wet or contaminated with ice, standing water, slush, snow or any other
deposit that results in reduced braking capability.

(Boeing 737 NG FCTM 2.13 Ground Operations, emphasis mine)
This sounds quite similar to the FAA definition of contaminated runways, so I would assume the same definition applies to wet or slippery in §121 and §135 operations as well.
The FCTM further says:

Slippery Runway Landing Performance
Slippery/contaminated runway advisory information is based on an assumption of
uniform conditions over the entire runway. This means a uniform depth for
slush/standing water for a contaminated runway or a fixed braking coefficient for
a slippery runway. The data cannot cover all possible slippery/contaminated
runway combinations and does not consider factors such as rubber deposits or
heavily painted surfaces near the end of most runways. With these caveats in
mind, it is up to the operator to determine operating policies based on the training
and operating experience of their flight crews.

(Boeing 737 NG FCTM A.27 Landing Roll - Factors Affecting Landing distance)
So it seems to be (at least in part) up to the operator to provide clear definitions on when exactly a runway should be considered slippery.

The Flight Safety Foundation has collected some more definitions, although from Europe, not the US:

Dry Runway
The European Join Aviation Authorities (JAA) defines dry runway as "one which is neither wet nor contaminated, and includes those paved runways which have been specially prepared with grooves or porous pavement and maintained to retain 'effectively dry' braking action event when moisture is present."
Damp Runway
JAA says that a runway is considered damp "when the surface is not dry, but when the moisture on it does not give it a shiny appearance."
Wet Runway
JAA says that a runway is considered wet "when the runway surface is covered with water, or equivalent, less than specified [for a contaminated runway] or when there is sufficient moisture on the runway surface to cause it to appear reflective, but without significant areas of standing water."
Contaminated Runway
JAA says that a runway is contaminated "when more than 25 percent of the runway surface are (whether in isolated areas or not) within the required length and width being used is covered by the following:

"Surface water more than 3.0 mm [millimeters] (0125 in [inch]) deep, or by slush or loose snow, equivalent to more than 3.0 mm (0.125 in) of water;

"Snow which has been compressed into a solid mass which resists further compression and will hold together or break into lumps if picked up (compacted snow); or,

"Ice, including wet ice."

(FSF ALAR Briefing Note 8.5 - Wet or Contaminated Runways)

That is helpful information, though by no means definitive. The Contaminated Runway definition is probably the most helpful. I don't recall seeing that definition in recent memory.


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How many aircraft types can a 135 pilot be assigned to?
Is there a limit to how many aircraft types a §135 operator may assign a pilot to fly? In other words, could a pilot type rated to fly—for example—a Learjet 75, Citation X, and Challenger 300 be assigned by the §135 certificate holder to fly all three of these types in §135 operations at any given time? Would that pilot be limited—for example—to only two types at a time for the purposes of §135 flight operations? I am not considering flight assignments that are to be conducted under §91. Is there a difference if the pilot is assigned as PIC or SIC?
I ask because my understanding has been that a §135 operator may assign a pilot to a maximum of two aircraft types at a time. However, I cannot find any documentation or discussion to support this.
Edit: To be clear, I am not asking about how many type ratings an FAA certified pilot is allowed to acquire in total (the answer to that question is: no limit). I am asking about what §135 operators are authorized to do, as far as assigning flight crew to various aircraft types.

Are you asking for a regulation that specifies a maximum, or are you asking specifically about airline procedures?

Does this answer your question? How many type ratings are pilots allowed to hold at once?

@GdD, no, I am familiar with that question, which deals with the pilot certification issue of how many type ratings an FAA certified pilot may acquire (answer: unlimited). My question is about hat §135 operators are authorized to do, as far as assigning flight crew to various aircraft types. I think I have made my question clear—though I acknowledge the issue is obscure, but I am open to suggestions of ways to clarify it?

I don't believe that there is any regulation that limits the number of assigned aircraft of pilots for a Part 135 operator. Any limit would probably be in the company SOP's.

@RonBeyer I misspoke. I meant to say NOT asking for regulation. I'm aware there are no such regulations. I will delete and replace that comment with the correct wording.

@RonBeyer I am not asking for regulation; I am asking for guidance such as that given in FSIMS. I am not asking about airline procedures; I am asking about what §135 operators are authorized to do.

I don't believe there is a limit in the FSIMS documents (or other FAA guidance) either... the issue is currency. The more aircraft a pilot is assigned, the more time they need to spend on currency requirements. This functionally limits the pilots to 1 or 2 types that they can keep current and still be useful as a revenue pilot. I'm guessing some of the training captains may have 3 or 4 assigned aircraft types.

There is no FAA regulation limit for the number of types a Part 135 pilot can be assigned to, providing all training programs are followed.  Insurance and safety auditing companies usually have guidelines requiring no more than 2 types to be assigned at a time so the 2 aircraft limit has become something of an industry standard.
There may be non-US regulations that address this issue.


text:
Are horizontal engine pylons generally shaped to provide lift (in either direction)?
Most civil multiengine jets and some civil multiengine propeller aircraft have engines mounted in nacelles on the ends of pylons extending some distance away from the wing or fuselage.  Wing-mounted engine pylons generally extend vertically from the lower (or occasionally upper) surface of the wing; in contrast, fuselage-mounted engine pylons tend to stick out horizontally from the (almost always aft) fuselage.
In some cases, this horizontal pylon surface can get quite large:

(Image by Arjan Meijer at Twitter, showing a propliner under development by Embraer with turboprops on empennage-mounted nacelles, necessitating quite long pylons to allow the propellers to clear the fuselage.)
Additionally, at least one airliner had control surfaces mounted on the engine pylons, although these were only used as a stall-recovery aid.
On aircraft with horizontal engine pylons, are the pylons usually shaped to produce lift (either up or down)?

That plane is a beauty.

Like a flat plate, the horizontal pylons will generate lift at higher Angle of Attack, with little matter as to how they are shaped. Aerodynamic optimisation of the pylons and the nacelles during the design phase are listed in Torenbeek section 6.5.2 as follows:

Avoiding drag problems due to boundary layer separation in the divergent portion of the convergent-divergent channel formed by the nacelle, the pylon and the adjacent fuselage wall.
Configuring the nacelle behind and above the wing to create an effective Whitcomb-body effect, and increase the drag-critical Mach number of the aeroplane.

Since the nacelles are located behind the aerodynamic center of the wing, they will cause the aerodynamic center to move backwards. This stabilizing effect is partly compensated by an increment in the downwash at the horizontal tailplane due to the low effective aspect ratio of the nacelle/pylon combination.

At large angles of attack, particularly when the airflow over the wing has separated, the wake created by the nacelles and the pylons may greatly reduce the effectiveness of the horizontal tailplane. For this reason the location of the engines will be a factor in connection with the deep stall problem (cf. Section 2.4.2.).

(3. and 4. are direct citations.) The low aspect ratio of the pylon/nacelle combination creates problems, unlike the stabilons of the Beech 1900-D which alleviate problems with deep stall.
Cropped photo from Airliners.net
So the pylons are aerodynamically optimised, and lift generation is part of the optimisation process. And as mentioned in this answer: deflected thrust counts as lift as well.


text:
Why aren't quadjets required to remain controllable after a sudden, simultaneous failure of two engines on one side?
For all multiengine jets, it must be possible to maintain directional control of the aircraft in the event of a sudden failure of one engine in flight, with the other(s) firewalled, down to not far above the 1-g landing-configuration stall speed, without having to bank more than five degrees away from the dead engine.  For jets with three or more engines, the aircraft must, additionally, remain flyable if a second engine fails after the aircraft has been trimmed for one-out flight, but it is not required to cater to situations involving the simultaneous failure of two engines on the same side of the aircraft:

(b) It must be possible to make a smooth transition from one flight condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane limit-load factor under any probable operating conditions, including—
(1) The sudden failure of the critical engine;
(2) For airplanes with three or more engines, the sudden failure of the second critical engine when the airplane is in the en route, approach, or landing configuration and is trimmed with the critical engine inoperative; [14 CFR 25.143; regulations in other jurisdictions are similar.  My emphasis, showing that, for the two-engine-out controllability demonstration on a plane with more than two engines, the airplane is allowed the chance to retrim for one-engine-out flight before the second engine is failed.]

However, it is easy to think of situations that could take out two engines on the same side of a quadjet1 simultaneously, or very nearly so, and, indeed, a great many accidents of this type have occurred over the years (often as a result of uncontained engine rotor bursts [which are, to a degree, an inevitable part and parcel of the use of turbine engines on aircraft] or engine pylon failures [engine pylons walk a fine line between being too weak to carry the engine without fatigueing rapidly, and not being weak enough to allow the engine to safely break away in a crash or hard landing rather than tearing open the wings’ fuel tanks]), often with the additional insult of collateral damage (sometimes quite severe) to the aircraft’s flight controls and/or the structure and profile of the wing itself:

AF030 (747-100, August 1970): The #3 engine suffered an uncontained turbine rotor burst due to excessive and abnormal wear resulting from improper engine assembly.  Turbine fragments were ingested by engine #4, damaging it beyond repair; fortunately, it did continue to operate until shut down after a safe landing.
LO007 (Il-62, March 1980): The #2 engine suffered an uncontained turbine rotor burst due to the failure of a defective engine shaft aggravated by insufficient maintenance.  Turbine disc fragments, ejected at high speed, shot into and destroyed the #1 engine (and also the #3 engine, located on the opposite side of the fuselage), and also disabled critical flight controls, causing the aircraft to enter an uncontrollable dive and crash; however, had the ejected fragments taken a slightly different trajectory, leaving the flight-control linkages intact, the loss of engine power would have been the most pressing concern.2
LO5055 (Il-62M, May 1987): As in the previous case, the #2 engine suffered an uncontained turbine rotor burst due to an engine shaft failure (this time due to the failure of an improperly-assembled shaft bearing), which also disabled the #1 engine.  Unlike in the previous case, the aircraft was able to maintain flight for a considerable length of time before flight-control damage, aggravated by a rapidly-spreading fire, caused a loss of control and a crash; had the aircraft managed to reach an airport, the loss of engine power could have caused considerable handling difficulties.
UA811 (747-100, February 1989): The aircraft suffered an explosive decompression due to an uncommanded opening and separation of the forward cargo door, resulting from the door having (unbeknownst to the crew or ground personnel) become partially unlatched on the ground, due to one or more short circuits in the door’s wiring combined with a weak and ineffective safety mechanism which failed to prevent the latch mechanism from rotating almost to the fully-unlatched position.  Cabin debris, pieces of aircraft structure, and nine passengers separated from the aircraft, considerable portions of which were ingested by the #3 and #4 engines, causing catastrophic3 damage to both engines (immediately destroying the #3 engine’s ability to produce thrust, and critically damaging the #4 engine and setting it on fire) and forcing the flightcrew to shut both engines down; fortunately, the flightcrew were able to land the aircraft safely without additional fatalities, despite major structural damage to the aircraft, the unavailability of the #3 and #4 engines, and an asymmetric flap configuration resulting from debris damage to the pneumatic duct powering the right outboard krueger flaps.
CI358 (747-200, December 1991): The #3 engine and pylon separated from the aircraft due to the fatigue failure of the midspar pylon-to-wing attachment fittings.  The separated engine/pylon combination then struck the #4 engine, causing it to separate as well; the flightcrew lost control of the aircraft while attempting to return to the airport for an emergency landing, and it crashed.
Trans-Air 671, reg. 5N-MAS (707-300C, March 1992): The #3 engine and pylon separated from the aircraft due to a failure, during an encounter with severe turbulence, of the pylon attachment fittings resulting from fatigue damage that went undetected due to insufficient inspection requirements.  The separated engine/pylon combination then struck the #4 engine, causing it to separate and producing a fuel leak which ignited a wing fire during approach; the flightcrew managed to land safely (although the aircraft ran off the side of the runway during the last part of the rollout), but the aircraft was damaged beyond repair by fire.
TAMPA, reg. HK360 (707-300C, April 1992): As in the previous case, the #3 engine and pylon separated from the aircraft (this time shortly after takeoff, during initial climbout) due to a failure of the pylon attachment fittings resulting from fatigue damage that went undetected due to insufficient inspection requirements.  Although the separated engine/pylon combination again impacted the #4 engine, the latter engine, fortunately, did not separate from the aircraft, which landed safely and was later repaired and returned to service.4
LY1862 (747-200, October 1992): Similarly to the CI358 case, the #3 engine and pylon separated from the aircraft due to the fatigue failure of the midspar pylon-to-wing attachment fittings, this time due, in part, to a design defect in the fusepins holding the fittings together, which rendered the fusepins susceptible to accelerated fatigue cracking.  Again, the separated engine/pylon combination struck the #4 engine, knocking it off as well; additionally, a large section of the leading edge of the right wing was torn away and the aircraft’s hydraulic systems were damaged.  Control of the aircraft was lost during an attempted emergency approach and landing, causing it to crash.
AF4590 (Concorde, July 2000): During takeoff, the aircraft's left main landing gear ran over an item of debris shed by a prior aircraft, causing one of its tyres to burst; ejected tyre debris impacted the aircraft, severing electrical wiring in the landing-gear bay and (indirectly) rupturing a fuel tank, with the escaping fuel then being ignited either by arcing from the severed wiring or by contact with high-temperature engine components.  The #1 and #2 engines both surged and lost thrust due to ingestion of superheated gasses (as well as, for the #1 engine, ingestion of tyre debris), but partially recovered (the #1 engine much more rapidly than the #2 engine) before surging again due to renewed superheated-gas ingestion; following the second surge, the #1 engine again recovered to near-normal operation, but the #2 engine was shut down due to a fire warning.  The loss of engine thrust, combined with the inability to retract the aircraft's landing gear (resulting from tyre-debris impact damage to the left main landing gear doors), left the aircraft unable to gain speed or altitude, and the ongoing wing fire progressively damaged the left wing, eventually liberating fragments of aircraft structure which were ingested by the #1 engine, causing a final surge and irrecoverable loss of thrust.  The final loss of thrust from the #1 engine, combined with progressive fire damage to the left wing's flight controls, caused a rapid roll and yaw to the left; the flightcrew attempted to compensate by reducing thrust on the #3 and #4 engines, but were unable to prevent a loss of control, and the aircraft crashed.
CU201 (Il-62M, April 2008): The #2 engine suffered an uncontained rotor failure for reasons not stated (what is it with Il-62 #2 engines?).  Ejected fragments damaged the fuel lines to the #1 engine, forcing it, too, to be shut down, and igniting a fire; the flightcrew made a successful emergency landing, but the aircraft was damaged beyond economical repair.
QF32 (A380-800, November 2010):  The #2 engine suffered an uncontained turbine rotor burst due to heat damage from an oil fire resulting from the fatigue failure of an improperly-manufactured engine oil pipe.  Ejected turbine disc fragments damaged the aircraft’s primary and secondary flight controls, ignited a fire in a wing fuel tank (which self-extinguished before the aircraft’s safe landing), and severed the control cables for the #1 engine, preventing the flightcrew from changing the engine’s power setting or shutting it down; had the fragments been released onto different trajectories, they could instead have struck the #1 engine pylon and severed the engine’s main fuel line, causing the engine to flame out due to fuel starvation, or been ingested into the #1 engine, damaging or destroying its ability to produce thrust.
Omega 70, reg. N707AR (707-300B modified as an aerial-refuelling tanker, May 2011): The #2 engine and pylon separated from the aircraft just after liftoff due to a failure of the pylon attachment fittings resulting from fatigue damage that went undetected due to a prior erroneous maintenance-log entry which indicated that the fatigue-prone fittings used on the aircraft had been replaced with fittings not requiring frequent inspection for fatigue cracking.  The separated engine/pylon combination then struck the #1 engine, inflicting damage which effectively disabled the engine (although it did continue to run, albeit ineffectually); the flightcrew rejected the takeoff, but the aircraft overran the runway and was destroyed, primarily by fire (although all three flightcrew members were able to evacuate safely before the fire spread to the cockpit).

Given the many scenarios which could lead to a simultaneous or near-simultaneous failure of two ipsilateral engines on a quadjet, why are quadjets only required to demonstrate controllability if two ipsilateral engines fail one at a time (and there is sufficient intervening time for the aircraft to be retrimmed for three-engine flight), rather than being required to remain controllable even in the event of the sudden simultaneous failure of two ipsilateral engines?

1: For trijets, the thrust asymmetry produced by a failure of one lateral engine is the same as that produced by the simultaneous failure of one lateral engine and the centerline engine (in the latter case, the net thrust vector is offset twice as far from the aircraft’s centerline as in the former case, but the magnitude of the net thrust along said vector is half as great), while civil jet aircraft with more than four engines are extremely rare.
2: Early Il-62s also suffered from a rash of incidents where both engines on one side were shut down as a result of false engine-fire warnings, with the resulting thrust imbalance causing severe control difficulties; later modifications to the aircraft largely fixed this problem, but it did recur at least once (for reasons unknown) on the later Il-62M version, resulting in a fatal crash (SU411, July 1982).
3: Catastrophic for the engines, that is, not for the aircraft as a whole (as is obvious, given that the aircraft landed safely and was later repaired and returned to service, and that all of the occupants who were not sucked out of the aircraft in the initial decompression survived).
4: The information in the second sentence of this entry is not present in the NTSB report linked for that entry; it is, however, included, as background information, in the report linked for the entry for Omega 70 lower down.

I can't find a specific reference, but I'd guess it's like all things in aviation:a compromise. One could ask why the vertical stabiliser isn't required to handle a triple engine failure, or why the structural safety margin is 150% of maximum expected load rather than 200% or more.

Risk vs reward. Consider the number of 2-engine same-side failures you've found vs the number of single-engine failures over the time period you're reporting (1970-2011 - 41 years). Then compare that to the number of 0-engine failure flights that have happened during those 41 years. Like everything in aviation, as in life, there is risk and while there are cases where some risk can be mitigated, but the cost of doing so significantly outweighs the cost of not doing so. Yes, failure can be fatal, but it's so infrequent as to be an "acceptable risk".

Googling "quad jet" came up with this-- https://fusionflight.com/jetquad/ -- also brings to mind images of a quadcopter drone with a jet engine strapped on top, or a 4-wheeled ATV off-road vehicle with a jet engine strapped on somewhere-- not a big fan of this term for a four-engined aircraft--

Loss of two engines on one side on four-engine aircraft is taken into account in the design of the aircraft.
I'm not sure where the notion came from that a four-engine airplane can't handle two engine failures on the same side, but it's untrue.  In fact, on each of my captain checkrides in four engine airplanes, from piston to turbojets such as the 747, 2-engine operation, with two out on one side, is standard and required.
Loss of two engines on one side is a hand full, not because of insufficient rudder, but because of loss of performance, and changes in systems, as well as fuel asymmetry, etc.
The rudder on the 747 is several stories high; there's a lot of surface there.
Speed, flap setting, and runway options change with two engines out, particularly with a crosswing.
Another consideration with loss of engines on the same side on large airplanes is that aileron input may be required as well as rudder, and with large deflections, typically flight spoilers also deploy, increasing drag and decreasing performance.
If the question regards multiple engine failures during takeoff, one could take the question quickly to the point of diminishing returns by asking about various combinations of failures.  Why wasn't sully able to continue with both engines out (obviously, no engines)...there can certainly occur events which preclude continued flight.  For design certification criteria, addressing all of them, particularly those which are unrealistic, makes little sense.

The wording of 14 CFR 25.143 suggests that, although failure of two engines on one side is considered, failure of two on one side at the same time is not; before the second engine failure, the aircraft is assumed to already be trimmed for one-engine-out flight, which would not be the case if both engines on one side were to fail simultaneously.

The risk model used for aircraft design redundancy simply doesn't have to account for simultaneous multiple failures.  Two engines on one side going south at the same time in a critical takeoff phase (usually engine failure between V1 and V2) is beyond the 1 in a billion probability threshold for catastrophic events, so the rudder system won't be required to cater to it.


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Why are the A300/310’s electric pitch trim switches inhibited with the autopilot engaged?
The A300/A310, like most other aircraft (except for some small general-aviation aircraft), has an adjustable-incidence-angle horizontal stabiliser, which is used to trim the aircraft in pitch (for instance, to change the aircraft’s speed or compensate for shifts in its center of mass) without the need for large elevator deflections (which would increase the stress placed upon the elevator control linkages and actuators, shortening their lifespan, and, if the autopilot was flying the aircraft, would  result in large pitch excursions upon autopilot disconnect as the elevator returned to its neutral position).
There are three methods by which the horizontal stabiliser can be moved:

The A300/310’s autopilot, like those of most other autopilot-equipped aircraft, automatically trims the aircraft in pitch when engaged; it moves the stabiliser by applying power to a set of electric motors which rotate the stabiliser jackscrew, moving the stabiliser’s leading edge up or down.
In manual flight, the aircraft is usually trimmed by using two sets of electric trim switches (one on each of the two control yokes), which, like the autotrim system, apply power to a set of electric motors which rotate the stabiliser jackscrew.
As a backup, a manual pitch trim wheel is mounted on the center console between the pilots; this wheel is connected to the stabiliser jackscrew via a cable mechanism, and, when used, manually rotates the jackscrew directly.

If the autopilot is engaged, the electric pitch trim switches are inhibited, and cannot be used to trim the aircraft; the aircraft can only be manually trimmed by rotating the manual trim wheel, which disconnects the autopilot.  As a result, in the event of an autotrim runaway, the pilots need to take one hand off the yoke to manually trim the aircraft against the malfunctioning autotrim.  This used to be especially critical in two specific autopilot modes (LAND and GO-AROUND), where, prior to 1997, pulling or pushing on the yoke to use the elevators to manually counter the autotrim-induced pitching moment would not disconnect the autopilot if the aircraft was less than 400 feet AGL (and, originally, would not do so no matter what the height AGL); indeed, doing so would cause the autotrim to trim further and further against the pilots’ control inputs, exacerbating the problem at a time when maintaining pitch control of the aircraft was (due to the very limited altitude available with which to work with) far more critical than in most other phases of flight.
So why are the yoke-mounted electric pitch trim switches inhibited and inoperative whenever the autopilot is engaged?

Like with two human pilots, you want control1 to be explicitly in one hands. With autopilot, it's the same: it should be either autopilot or you.
In the case of 'breaching' the normal transfer protocol for whatever reason ("I have control" - "You have control", which in case of autopilot would be the autopilot disconnect button), there are two possible courses of action when the pilot just starts to control the aircraft:

Immediately give control by explicitly disconnecting the autopilot.
Keep control by ignoring/overriding the pilot as much as possible.

Apparently, Airbus espoused the second strategy. It made sense for them to ignore the pilot (whether for trim or main control) until s/he explicitly requests control. (There is not much the aircraft can do when the pilot starts to trim the wheel manually, so it still disconnects).
If the trim switches were not ignored, there could be two options.

Disconnect the autopilot. But this changes the whole ideology, and other things would need to be changed to be consistent.
Just change the trim. But the autopilot (which is still in control) would have to fight against it in order to keep doing its job (e.g. flying level), either by trim or elevator.2 This makes no sense and creates dangerous confusion.

Arguably, completely ignoring the pilot is not a very good idea, so Airbus had to change the algorithm at least in some situations.

1 By 'control' I mean guidance control, excluding things like stability augmentation systems.
2 Unless this is a simple autopilot which does not actuate trim at all and may then need help from the pilot. This is the case for some GA aircraft, but not for A300/310.

I like this, a @sean question without footnotes, and an answer with them!. Well played!

"It made sense for them to ignore the pilot (whether for trim or main control) until s/he explicitly requests control" - ...the pilots actively overriding the autopilot isn't explicit enough?

Just starting to move controls (including trim switches) does not count as 'explicit'. Like with transferring control between humans. At least in this kind of ideology, which puts autopilot on equal terms with the pilot, as opposed to it being a 'slave' or 'assistant'.


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Are 737 pilots required to train in manual-reversion flight?
All jetliners prior to about 1970 had flight controls that could, if need be, be manually operated without the use of any hydraulics:

Some, such as the DC-9, had manual flight controls with hydraulic boosting available; the flight controls were manually operated even in normal flight, with the hydraulics providing additional force to assist in certain situations requiring very large control inputs.
Others (707, 727, 737) had hydraulic flight controls with manual reversion available; the flight controls were normally operated hydraulically, but would revert to backup manual control if hydraulic pressure was lost.

After the first widebodies entered service in the early 1970s, which had no provisions for manual control, instead assuming that their triple-or-quadruple-string hydraulics would provide enough redundancy that a total hydraulic failure could never occur (an assumption which proved unwarranted), aircraft manufacturers mostly stopped including manual control capability (even for narrowbodies where it would have been easy to include); nowadays, the only manually-controllable jetliners still in commercial service in significant numbers are the DC-9 (produced from 1965 through 2006; hydraulically-boosted1 manual controls) and the 737 (produced since 1967;2 manual-reversion capable hydraulic controls).
The DC-9 holds no surprises for its pilots in full-manual mode, as this is its normal mode of operation (the hydraulics only kick in in a few extreme situations that would never be encountered in normal flight).
The 737, on the other hand, behaves considerably differently in manual-reversion flight than it does normally:

First and foremost, manual reversion is available only for the ailerons and elevators; the rudder and spoilerons have no provisions for direct manual control.3
The control forces for the aircraft’s horizontal-stabiliser pitch-trim system are much higher when using the manual trim wheel than with the normal electrohydraulic trim (this is especially prominent for the 737 NG and MAX, which have a smaller manual-pitch-trim wheel than the 737 Original and Classic, reducing the mechanical advantage provided by the wheel; in some circumstances, the force required to turn an NG/MAX's manual-pitch-trim wheel may exceed human capabilities).
Control of the ailerons and elevators in manual-reversion flight is by servo tabs that, when deflected, produce aerodynamic forces that move their respective control surfaces; in contrast, when hydraulic pressure is available, the control tabs are mechanically locked to their respective surfaces and move with them.  Consequently, the effective area of the control surfaces is slightly lower in manual-reversion flight (as the control tab, in order to move its respective elevator or aileron, is deflected in the opposite direction to the desired aileron or elevator deflection, rather than functioning as additional elevator or aileron area), somewhat increasing the amount of control-surface deflection required to produce a given aircraft response, and slightly decreasing the aircraft’s maximum pitch and roll control authority.
Other, relatively-minor expected effects of the different methods of controlling the control surfaces in hydraulic and manual-reversion flight would be a change in the control surfaces’ damping characteristics and a slightly-different flight-control force-response curve (as the control forces experienced by the pilots in manual-reversion flight are a direct product of the aerodynamic forces on the aileron and elevator control tabs, which would be more sensitive to aerodynamic factors other than airspeed, such as a nonzero sideslip angle, than would the aircraft’s artificial-feels computer, which provides yoke and rudder-pedal force feedback in hydraulically-powered flight).

Given these differences in aircraft handling between normal and manual-reversion flight, are 737 pilots required to undergo training on flying the 737 in manual reversion (as is the case for other situations affecting aircraft handling, such as an asymmetric loss of engine thrust, a no-flap landing, a stall and recovery therefrom, a jammed pitch-trim system, etc.)?

1: Albeit only for the elevator, and only in certain stall-recovery situations where the required down-elevator force is greater than what the aerodynamic downforce from the elevator control tab can provide on its own.
2: Albeit currently temporarily paused.
3: A small amount of rudder deflection is attainable even without any hydraulic pressure, due to the design of the 737’s rudder system; however, this requires the application of an extreme amount of force to the rudder pedals (approximately 300 pounds4 per inch of rudder pedal deflection after the first inch, in addition to the additional force required to push the rudder pedals the initial inch required to take up slack in the rudder control system), and can only produce a very small amount of rudder deflection.
4: For context, the maximum force that an average pilot is physically capable of applying to an aircraft’s rudder pedals is generally around 500 pounds.

I am not sure what other organizations practice but I have been through simulator runs with a complete loss of hydraulics on the -800 and its something I never want to experience ever. The aircraft is still flyable, but now instead of being able to operate the yoke with ease, you will now find that it might even take two pilots to yank the control yokes and you have to do it with proper thought and gauge of where you want the airplane to be. I came out drench in sweat at the end of the session.
Asymmetric loss of engine thrust is a standard and we often go through it as part of your base checks in the simulators. All the non-normal profiles you have mentioned, I have gone through it as part of the type-rating programme.

Yes, B737 pilots are trained in controlling th aeroplane using manual reversion. Both the forces at the controls and the aeroplane response to flight control inputs are quite different from those of the hydraulically powered elevator/aileron set-up. The difference in feel characteristics is quite pronounced, as we found in the past from flight control measurements of an actual B737-200.

Roll
The powered ailerons have a friction force of about 2.5 lbf (11 N) in either direction. This friction force needs to be overcome by the applied pilot force at the wheel, after which the roll control circuit moves the aileron. Feel characteristic is then the mechanical feel spring, the slope of which does not change with airspeed.
In manual reversion, the circuit friction is about 10 lbf (45 N) in either direction. So from neutral, apply 45 N wheel force to the right in order to overcome circuit friction and move the aileron tab. When then rolling the other way, apply 90 N (!) of force to start deflecting the tab the other way. Feel characteristic is then the artificial feel spring mentioned above, plus the airforce gradient at the tab, higher gradient at higher airspeed. Requires a lot of force at speed, plus no direct control in the much higher friction band.
Pitch
Powered. Basic circuit friction is about 5 lbf (23 N) in either direction. The mechanical feel spring is a q-feel system, as also described in this answer, about 10 lbf/deg at 400 kts.
In manual reversion, the circuit friction is again much higher at 15 lbf (70 N) in either direction. Plus the airforce gradient is about double the force to deflect the elevator tab, about 20 lbf/deg at 350 its.

Overall, significally different and definitely a topic for flight simulator training. But upon checking the type rating curriculum of the B737-NG, I could not find a direct reference to manual reversion.

This is great information on how the forces differ, but do you have a source for the requirement of manual reversion training during the type rating?


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Why did the dividing wall separating the engine intakes of early twin-engine Westland Wessexes cause difficulties with intake anti-icing?
The Rolls-Royce1 Gnome-engined variants of the Westland Wessex helicopter family (i.e., the twin-engined versions)2 draw air for both engines from a common intake (having been designed prior to the advent of requirements for physical separation of helicopter engine intakes), meaning that a destructive failure of one engine can potentially throw debris into the intake for the opposite engine, potentially disabling it as well; this was considered as one possible contributing factor (among many other possibilities) to the total loss of power that culminated in a fatal 1981 crash of a Gnome-engined Wessex 60, and had definitely occurred on four instances before the 1981 crash (although, in each of these four prior cases, the second engine, although damaged, continued to operate).
Early Gnome-engined Wessexes had a dividing wall separating the left and right engine intakes; however, this was removed after some time, due to difficulties it apparently caused with anti-icing the intakes:

However, in the event of compressor damage it is possible for the Gnome engine to eject debris forward out of the compressor which, in the Wessex 60, may be ingested by the other engine since the intakes are not separated.  Rolls Royce (RRL) were aware of four cases in which both engines in a Wessex had been damaged in this way, although in none of the cases was the power remaining available insufficient for continued flight.  Whilst the original design incorporated a dividing wall which achieved separation of the compressor intakes difficulties in achieving a satisfactory anti-icing standard led to its removal in a modification approved by the CAA but not by RRL.  The possibility therefore exists that a failure in one engine could, by cross ingestion, lead to a complete loss of power.  Since the Wessex 60 was certificated BCARs have been revised, and now require engine intakes to be independent of each other.  [AIB3 Aircraft Accident Report 4/83, pages 21-22 (pages 25-26 of the PDF file of the report); my emphasis.]

Why did the original dividing wall cause anti-icing difficulties?  Was it too thin to accommodate the wires or bleed ducts required to anti-ice it?

1: Formerly de Havilland.
2: Very early Wessexes instead used a single Napier Gazelle engine.
3: Not a typo - the AIB didn’t become the AAIB until November 1987.


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How does the paint on a F-35 absorb radar waves instead of reflect them?
I was doing some research for a project I am doing at school about military aircraft and I read that the F-35's paint is able to absorb radar waves instead of deflect them.
How does paint absorb radar waves?

https://en.wikipedia.org/wiki/Radiation-absorbent_material  https://www.sciencedirect.com/topics/engineering/radar-absorbing-material

For a radar beam to be reflected by an object (thereby producing a return) requires that there be an impedance mismatch between it and free space. The characteristic impedance of free space through which radar pulses travel is about 330 ohms, which is way different from that of a metal airframe. This means that if a radar pulse strikes that airframe, almost all of the pulse will bounce off it and almost none of it will be absorbed into the airframe.
On the other hand, if that pulse strikes something with the same impedance as free space or close to it, almost none of it will be reflected and almost all of it will be absorbed by that object.
Now we note that if the matched-impedance object possesses a certain amount of electrical resistance, the electric currents induced in it by the incoming pulse will be dissipated by its resistance, preventing those induced currents from producing an outgoing electromagnetic wave i.e., a return.
So stealth paint works by absorbing the incoming pulse and then dissipating it.
This process is not perfect, and so stealth designers strive to avoid flat surfaces and sharp 90 degree corners in the profile of the plane, so any returns generated will be sent off in a direction that does not point straight back to the radar station.


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Why are doors 3-left and 3-right not available during water evacuation in an A330?
I've seen 2 safety videos of A330s - one with Nepal Airlines and another of (now defunct) Jet Airways.
Both of them say that doors 3 left and 3 right cannot be used in a water evacuation.
Why is it so?

It depends on the type of door that is installed at position 3L and 3R. Airbus offers the A330 with a type 1 door, which is a smaller emergency exit door, and optionally with a full type A door. Only the type A door emergency escape slide can be used as a raft, therefore evacuation on water should not be performed through 3L and 3R when only a type 1 door is installed:

(Airbus Aircraft Characteristics - A330)
That is why some operators like Emirates (left) instruct passengers not to use doors 3L and 3R on water, but others like Air Transat (right) allow this:

(image sources: Emirates, Air Transat)
If you compare pictures of the Emirates and Air Transat A330s, you can see the larger type A door on the Air Transat:

(image sources: Emirates, Air Transat)

Thank you! But why do airlines opt for such variants? During water evacuations is it not vital to empty the plane ASAP as water may keep on entering the plane? Is it not safer to have 8 exits with rafts as opposed to 6?

@HarikrishnanM What type of emergency exists are installed has an impact on the exit limit, which is the maximum number of passengers allowed on the aircraft. This means airlines with lower density cabins (with larger first and business class seats or more leg room) don't need the larger exits. After a successful water landing (aircraft doesn't break apart), you actually have quite some time for an evacuation.

So since Transat had denser seat configurations on board, they are mandated by aviation law to make more exits available for evacuation. On the other hand Emirates had the opposite, thus it's enough to put just six. I get it @Bianfable, thank you!


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In aircraft where the thrust reversers are not locked out when airborne, is it permissible to go around after reverser deployment?
In general, a go-around, in a jetliner, must either be performed before thrust reverser deployment, or not at all.

This is because attempting a go-around after reverser deployment may result in loss of control of the aircraft.
Loss of control is a possibility because one or more of the reversers could fail to stow during the attempted go-around, potentially resulting in an asymmetric-thrust situation beyond what most jetliners are designed to handle.
This is because the reversers take several seconds to fully stow once deployed, and the aircraft could easily lift off before this happens, in which case any not-yet-stowed reverser buckets or clamdoors will be blown back to their fully-deployed positions by the aerodynamic forces on said piece(s) of reverser hardware.
Lifting off is relevant because, when the aircraft lifts off, the reverser actuators are automatically locked out and depressurised.1
The reversers are locked out when airborne to minimise the risk of an uncommanded in-flight reverser deployment, which, for aircraft not certified for in-flight thrust reversal, is generally bad.

However, some aircraft are capable of, and certified for, the safe use of reverse thrust in flight (typically to steepen descents by using reverse thrust as an airbrake [DC-8, Trident, Concorde, C-5, C-17], or to shorten the landing roll by deploying the reversers while still airborne rather than having to wait until after touchdown [Trident 1C, Il-62, Tu-154]).

To allow this inflight use of reverse thrust, the reversers on these aircraft are not locked out when airborne.
As such, the reverser actuators remain pressurised even after the aircraft lifts off.
Consequently, even if the aircraft lifted off before all reversers had fully stowed, the reversers would simply continue to stow.
As a result, lifting off with one or more reversers still in transit would not produce a significant risk of a severe asymmetric-thrust situation.
Even if, for some reason, a reverser did fail to stow, resulting in thrust asymmetry, aircraft certified for inflight reversing are required to remain controllable even with full forward thrust on one side and full reverse thrust on the other, at least for long enough to shut down the reversed engine.
This would appear, for aircraft certified for inflight reverser use, to essentially eliminate the danger of loss of control (absent other serious failures) in the event of a go-around after thrust-reverser deployment.

This would be especially important for aircraft like the Tu-154, Il-62, and Trident 1C, which routinely deploy their reversers before touchdown; if going around after reverser deployment was prohibited for such aircraft, this would seem to completely preclude very-low-altitude go-arounds with these types.
Are aircraft certified for in-flight thrust reversal (and, thus, not equipped with an in-flight reverser lockout mechanism) allowed to go around even after the thrust reversers have been deployed?

1: There is generally an override switch in the cockpit that can be used to restore pressure to the reverser actuators even when airborne (its main use is to force the reversers to remain stowed if one or more should come unlocked in flight, or to restow then in the event of an uncommanded in-flight deployment), but locating and actuating this switch would take precious seconds which might not be available in the event of an asymmetric reverser deployment at low altitude in an aircraft not certified for the inflight use of reverse thrust (especially as, during the time spent with their actuators depressurised, the deployed reverser(s) would be blowing back to the fully-deployed position, taking them further and further from the stowed position).

Re "and the aircraft could easily lift off before this happens, in which case any not-yet-stowed reverser buckets or clamdoors will be blown back to their fully-deployed positions by the aerodynamic forces on said piece(s) of reverser hardware" - you are saying that if a/c lifts off before reverser buckets /clamshell doors are stowed, they are certain to be blown fully open?  Why?  Is it due to jetwash and therefore more related to throttle position than to liftoff?  Or - ???

@quietflyer - Both engine thrust and the aircraft's forward motion through the air generate rearwards airloads on the reverser moving bits; more here.

An aircraft approaching to land with a reverser deployed or unlocked, particularly one that's deployed unintentionally, will be at idle power, or shut down on the deployed reverser.
A go-around or missed approach is conducted in the same manner as if the engine is shut down for any other reason.

I don't think this really answers the question - yes, if you had a malfunction prior to the go-around, you'd have shut down the engine with the malfunctioning TR. But he's asking how would the go-around be conducted

I answered the question correctly.  It would be very unwise to go missed approach with a reverser deployed, but if it were deployed, and a go-around required, the same procedure is used as a go around with that engine inoperative.   The engine is shut down.  The go-around is conducted on the remaining engine(s).  Increasing airspeed will increase the drag effects of the engine with the reverser deployed.  In my current airplane, after the basic procedure is performed, the FCOM states, "Continue use of affected engine at Captain's discretion."

If the engine is still in operation, which might be the case only if there is no buffet, aircraft behavior doesn't indicate the reverser is actually deployed, or other evidence indicates its not actually deployed, then it will be used as needed; this presupposes that it's only an indication problem.  Otherwise, if the engine has been shut down, the missed approach is flown the same as any other missed approach with that engine shut down, being mindful that the drag increase is more than with an engine simply shut down.  Flap use may be restricted during the approach.


text:
Why does the CRJ100/200’s FMS miscalculate temperatures at altitudes in excess of 36k feet?
The CRJ100/200’s flight management system (FMS) apparently is not to be used to calculate engine thrust settings when the aircraft’s altitude exceeds 36,000 feet, due to internal calculation errors at altitudes this high:

The Pinnacle Airlines CRJ FCOM, volume 2, Performance, pages 50 through 52, dated June 2002, presented altitude and climb capability charts. Pilots were required to consult these charts anytime a flight was operating above 36,000 feet because of a flight management system (FMS) limitation above that altitude.77  [...]
[...]
77 FCOM volume 2, Operating Limitations, pages 30 and 31, dated June 2004, stated that “the FMS calculated thrust setting must not be used if the pressure altitude is greater than 36,000 feet.” The Bombardier chief pilot stated that the reason for the FMS limitation above 36,000 feet was because of the inaccurate calculations above that altitude. Further, according to Bombardier, at altitudes above 36,000 feet, the conversion from static air temperature to the International Standard Atmosphere (ISA) deviation is incorrect within the FMS, resulting in an error in the N1 indication at those altitudes.  [...]  Bombardier’s Flight Planning and Cruise Control Manual and Quick Reference Handbook contain charts that show the proper N1 indication for altitudes between 36,000 and 41,000 feet.  [NTSB/AAR-07/01, page 33 (page 45 of the PDF file); footnote numbering in original; my emphasis.]

Given that 36 kilofeet is well below the CRJ100/200’s maximum operating altitude,1 it seems surprising that the aircraft’s FMS was not programmed correctly for altitudes beyond 36k feet, that this wasn’t caught very early on, and that the FMS  software was not updated to correct this bug once it was discovered; why was the FMS misprogrammed in the first place, and why wasn’t it fixed?

1: The maximum operating altitude for first-generation CRJs is 41 kft, a full 5,000 feet higher.

Ah yes the famous Pinnacle "we're gonna hit trees dude" crash.  They ran into a meth lab in a garage behind some rural houses, which caused the post crash fire.  That incident drove a change to production test procedures, requiring core lock checks with numerous windmill relights, and also introduced high altitude stall recovery training during recurrent.

I was type rated in 2008 and I don't ever remember having to consult the thrust setting tables to get MCT above FL360, so I expect a software update fixed that particular problem after the Pinnacle event.  The 200 is a pig above about FL370 if loaded and they rarely go much higher.  The Pinnacle crew should have had no problem going to 410 if they'd used the proper procedure, as they were quite light. You just leave it Mach Mode and let it take its time.

The reason is that the tropopause is at 11 km (36 089 ft) in the International Standard Atmosphere. At the tropopause, the temperature lapse rate of the atmosphere (how temperature changes with altitude) has an abrupt change: the ISA value is -6.5°C / km (-1.98°C / 1000 ft) below and then suddenly changes to 0°C / km (meaning temperature suddenly stays constant).
The FMS probably converts SAT to ISA deviation based on a fixed lapse rate of -1.98°C / 1000 ft, which means the conversion is wrong above that altitude. Only a Bombardier engineer (or someone involved in the Collins FMS used on the CRJ) could tell you the exact reason why. Based on John K's comment, it seems to have been fixed after the accident.
Note that the actual tropopause altitude can vary (usually between 9 km at the poles and 17 km at the equator).


text:
Why is the Tu-204 virtually immune to wing and tail icing?
Atmospheric icing is extremely hazardous to heavier-than-air aircraft, as it badly disrupts their ability to generate aerodynamic lift (the inherent roughness of accreted ice encourages the airflow to separate from the upper surface of the wing, causing the aircraft to stall at a much lower angle of attack, and a much lower lift coefficient, than it would otherwise) and greatly increases aerodynamic drag (the rough, non-streamlined surface of the ice has much the same effect on the aircraft’s motion through the air as gluing a big sheet of 00-grit sandpaper to your butt would have on your motion down a playground slide).  As such, built-in anti-ice equipment (generally consisting of heaters using either engine bleed air or electrical-resistance heating elements, or of pneumatic deicing boots that mechanically dislodge ice) is generally a must for the wing(s), tail surface(s), and propeller(s) (if any) of airplanes intended to fly in icing conditions, in order that any accumulated ice can be melted or broken off before it can significantly affect the aircraft’s aerodynamics.  If these systems are inoperative, the aircraft must not be flown in icing conditions until its anti-ice capability is restored, and aircraft lacking these systems are generally forbidden from entering ice altogether.
The Tupolev Tu-204 is an unusual exception to this.  Its wing and tail surfaces are (supposedly) so resistant to ice accumulation that it can fly in heavy icing conditions without needing to be equipped with wing or tail anti-ice equipment:

...The wings and tails are relatively resistant to ice build-up, and as such anti-icing systems are not equipped.  Among today’s airliners the Tu-204 is the only one which does not require wing anti-icing systems.  During the test flight safety has been confirmed without the anti-icing system on the bearing surfaces and the aircraft obtained Russian and European certificates...  [Wikipedia, “Tupolev Tu-204”, section 1.1 (“Technology”).]

This seems like a rather suspect claim; atmospherically-generated ice has the well-documented tendency to stick to essentially whatever it hits (as long as it’s not warm enough to melt the ice off), no matter what its composition, shape, or surface texture.  Even if the Tu-204 goes the usual route of making the tail bigger so it works fine even when iced, this doesn't explain how they can get away with non-anti-iced wings; how does the Tu-204 supposedly manage to do this?

I love the analogy for the effects of ice on a wing!

It is not uncommon for tails not to have anti-icing. At least most (all?) Airbuses don’t have anti-icing on their tail surfaces although they do collect ice. Also leading edges of wings are only partially deiced.

Sean, I am always amazed about the nuggets you dig up. Thank you for sharing those!

Just like Teslas, being designed in California, perform worse in ice and snow than Volvos, Russian airplane designers pay more attention to icing than Western ones, where efficiency is paramount. And you can design for icing, mainly by selecting a large leading edge radius which keeps suction peaks low. In addition, large airplanes are proportionally less susceptible to icing.
From NASA:

Wings that are thin or have sharp leading edges are more efficient ice collectors. For this reason, smaller, thin airfoils may accrete more ice faster than larger, thick airfoils. A large transport aircraft will accrete proportionally less ice than a smaller aircraft traversing the same icing environment.

Also, if the leading edge radius of the wing decreases from root to tip (as it frequently does in swept or tapered wings), the ice accretion will be proportionately greater near the tip. When contaminated with ice, wings with this design may experience flow separation at the tip before the root. Note that this is exactly opposite the way clean wings are typically designed to experience flow separation. Thus, when you fly these types of aircraft, you could lose aileron effectiveness before total wing stall, increasing the probability of an uncommanded roll and greater difficulty in regaining control.

A further factor is the thrust margin of airplanes. Being a two-engined airplane, the Tu-204 has plenty of excess thrust to compensate for the addd drag of iced wings. Since icing occurs at moderate altitudes, the thrust margin there is considerable. The same is true of the B777 and the A330, of course.
But much is left to trial-and-error. Again NASA:

Some aircraft seem to be more susceptible to airframe icing than others. The reasons for this are not well understood and probably involve multiple factors. For example, there seems to be a complicated interaction between the details of the wing design (e.g., taper ratio, twist) and its relation to the fuselage.

And in Russia icing research is well established. From the website of the Central Aerohydrodynamic Institute (TsAGII)

In Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (part of Zhukovsky Institute National Research Centre) the considerable attention is paid to icing effect made on aerodynamics, stability and controllability of aircraft.

The T-101 windtunnel of TsAGII in Zhukovsky is specially equipped for icing studies and has been used in the design of most Russian airplanes. I could not find a confirmation but would be surprised if the Tu-204 basic design has not been extensively studied there.

Not that there aren't snowy places in Cali for Tesla to test their cars at, though...all they have to do is head up into the Donner Pass some winter ;)

"...Russian airplane designers pay more attention to icing than Western ones, where efficiency is paramount..."  Are you implying that this is due to the climate at the ground level or due to some historical, cultural, economic factors? (The rest of your answer is clear)

@paperskilltrees My experience is from the An-70 development: Russian standards were simply more demanding than Western ones. I attribute this not only to the extreme conditions for Soviet aviation in winter, but also (almost) limitless funding for testing. The An-70 was not only tested in snow and hail, but also for ditching qualities, something the A400M program left out. On a parallel track, the Russian K-36 ejection seat is the only one which fulfils all specs demanded by the USAF (Wright Patterson AFB writes those requirements). Go figure!

@paperskilltrees Of course, things have mightily gone downhill since 1991 ...


text:
Does the Boeing 737 NG have "5" radar altitude callout?
I was watching a video of a Boeing 737 NG land, and heard the "5" callout.
Is that an airline option or something?

I would be willing to bet that it's related to this question/answer, which says that if they maintain the same altitude (probably during the flare in this case) for more than four seconds, it will make a new announcement with the current altitude:  https://aviation.stackexchange.com/a/47098/69.  The airplane that I fly has a 10' callout, but on a couple of occasions over the six years that I've flown it, I've heard it call out 5', and thought that it was odd (I probably floated longer than normal and didn't realize that was the cause!).

Thanks for sharing the video link :) @Lnafziger in the video the callouts "50, 30, 20, 10, 5" all come very close together, so it cannot be related to that. I have also never read anything like that in a Boeing manual.

The Rockwell Collins EGPWS, that is probably the most widely used system (you can tell right away by the voice that sounds exactly like the character "Data" from Star Trek - Next Generation; I'd swear it's the same actor's voice) comes with the full range of callout altitudes/heights and airlines pick and choose which ones they want by "configuration strapping" settings (connector pin jumper configurations in the mounting tray) when the units are installed in the avionics bay.

Fo you have a link to the configuration mechanism? I've never heard of such mechanism and would like to learn more.

On older avionics there would be physical jumper hardware at the connector that provides on-off inputs or DIP switches on the back of the avionics unit.  On modern ARINC 429 avionics there is usually what is called a Configuration Strapping Unit (CSU) https://avionicsales.com/product/configuration-strapping-unit-822-1363-002-csu-3100/ which is a module full of DIP switches that do the "jumper" function (basically a mode on or off signal) for the various on-wing setup options.  Do some rummaging around on the web for CSU and you'll probably stumble onto some training material.

Configuration using DIP switches and hardware jumpers? What is this, 1992??? Oh, yeah, aviation... technology move slowly in the aviation industry - that is probably the latest update flying.

Don't know for sure, but on the latest avionics suites like Proline Fusion I'm pretty sure it's done by software.

Yes, that must be an airline option. My Boeing 737 NG FCOMv2 says (15.20.17 Warning Systems - System Description):

Approach Callouts
Radio Altitude Callouts
The GPWS provides the following altitude callouts during approach:

2,500 feet – TWENTY FIVE HUNDRED
1,000 feet – ONE THOUSAND
500 feet – FIVE HUNDRED
100 feet – ONE HUNDRED
50 feet – FIFTY
40 feet – FORTY
30 feet – THIRTY
20 feet – TWENTY
10 feet – TEN.

Note: Callouts at 1000 feet and 500 feet are based on barometric altitude above
the landing field elevation; callouts at 2,500 feet, and below 500 feet are
based on radio altitude.

The FIVE callout is not listed here and I actually never heard it (could you link the video?). But since not all airlines have all of these callouts, it must be an airline option.

Any idea why they switch from radio to barometric then again to radio? I'd have expected it to be barometric above a certain altitude then radio all the way down

@DeepSpace The 2500 feet callout is where the RA comes alive (it is also not displayed on the PFD before). It also warns you that you are now close to terrain (it is part of the Ground Proximity Warning System after all). The following callouts are barometric because above uneven terrain, this would not be very helpful in determining time until touchdown (1000 and 500ft are usually the altitudes at which you have to be stabilized in VMC and IMC respectively). The rest is RA again because now you are very close to the runway and more accuracy is needed.

I think you mean, stable at 1,000 in IMC and 500 in VMC, yes?

@RalphJ Oops, yes you're right of course, I mixed that order up.

This page says by default it is ...30, 20, 10, but "Customers can also request special heights, such as 60ft."

It depends on how long you flare. If it's over 4 seconds it'll call out with. I see it as the manufacturer's option as the airlines won't care about it.
I've noticed this too, I fly the Boeing 737NG-900 and from time to time if I flare for too long it'll call out with 5. I know this isn't helpful but thought I might give an opinion.

Thanks for your answer. At the end you state "give an opinion". If this is really just your opinion, then it doesn't qualify as an answer here (please take the [tour] and look through the [help], specifically on answering to see what we expect). If it is factual, then please feel free to [edit] your answer to remove that statement, and, if possible, back it up with a quote from a relevant manual (and a link to said manual, if it's available online, or at least note what document you're pulling from) that supports your answer.


text:
Can a super land without flaps/spoilers?
Can the Airbus A380 or Boeing 787 land safely without flaps/slats/spoilers or thrust reversers?

yeah they will come in overspeed and need a long runway to get to a stop

Will this overspeed and slow braking (to avoid overheating the brakes) cause the tires to overheat and blow? Some tires can overheat on extended taxi durations, and this contemplates a much higher taxi speed.

@SkipMiller if you "slow brake to avoid overheat", I would say that the chance of overheating is practically null, unless you are doing something else wrong.

For what it's worth, the Boeing 787 is not a "super." Its MTOW is less than even a 777 (all variants), let alone a 747. The 747 is still Boeing's heaviest aircraft. (A modified 747 was even used to carry 787 pieces, like its wings, around.)

My apologies, I thought the 787 was a super.

@Federico, at taxi speeds a heavy plane like a 747 at Max Gross has a limit as to how far it can taxi before the tires overheat.  It is not just the brakes!  So I am wondering if a landing with slow braking will overheat the tires not the brakes.  I don't know the answer.

@SkipMiller oh, never heard of such a limit, sorry.

Aren't most tire failures during pre-takeoff taxi and sometimes the takeoff roll? The plane is more heavily loaded than at landing, which heats up the tires. Extensive or very hard braking can cause tires to blow from brake heat (see my comment below).

@SkipMiller, if you're landing with no flaps, then you have a LOT of energy to get rid of, and unless you have enough runway that the thrust reversers can get rid of most of it, then quite a bit of energy IS going into the brakes.  So they're going to be hot.  That's just what's going to happen with most no-flap landings.  Braking "slowly" won't help much -- you have some amount of kinetic energy that needs to be absorbed by the brakes, so whether it's absorbed over 10 seconds or 30 seconds, it's all going into the brakes. If you have to land no-flap, then hot brakes is probably a given.

But then you have also more time to dissipate that energy

Even the largest commercial airliners are able to land without flaps, since flap failures do happen occasionally. See a report here where an A380 landed with no flaps. This was at the Auckland, New Zealand airport, where the runway is 3,635 m (11,926 ft) long.
The pilots have checklists to follow in the event of issues with flaps, which include information about what speeds they should fly with what amounts of flaps. They simply land at a higher than normal speed. The brakes can end up getting hotter than normal, so they may have to stop and let them cool or have them inspected by emergency services. The tires are designed to deflate with fusible plugs before high temperatures would cause them to blow.
Aircraft are also tested to make sure they can reject a takeoff at high weights (higher than normal landing weights) using no thrust reversers. Here is a video of the 747-8 doing this test.

I've never heard about the designed-in tire deflation, is there an article I can read?

@CGCampbell Check this video out http://www.youtube.com/watch?v=qc_v6tXsv6g (same as posted above). At the end of the test they mention and show the deflation of the tires due to heat.

PBS had a multivolume video series (4 or 5 tapes) on the design, construction, and testing of the 777. The torture tests of brake overheating caused the fusible plugs to blow, so that fire crews wouldn't be endangered by exploding tires.

@PhilPerry I think this clip is from that series, but I liked the newer one better. https://www.youtube.com/watch?v=9nA7B-JWt3M

@PhilPerry Unlike the A340-600 RTO test, where the tires did explode. Some selected quotes: "It's not an important fire." "Bring the stairs." "Bring the stairs, now!"

@CGCampbell, see also: What's the difference between tire deflation & explosion

Specific information can be difficult to come by, and each airline may have their own guidance on the subject. I wasn't able to find anything for the 787, but for the according to one 777 crew handbook I found, flaps up landing was not part of certification:

All Flaps and Slats Up Landing
The probability of both leading and trailing edge devices failing to extend is
extremely remote. System reliability and design have reduced the need for some
traditional non-normal landing procedures. As a result, an all flaps up landing
NNC was not required for airplane certification and does not appear in the AFM
or in the QRH.

Basically this means that a demonstration of a no-flaps landing was not required during certification, so no specific guidance appears in the official handbook, and the manufacturer makes no claim that it can be done safely.
None of the Boeing 787 handbooks I found had official procedures for a flaps-up landing either.
That doesn't mean that it can't be done, but pilots are "on their own" so to speak, and the airplane may not be usable afterward.[*]
But the basic procedure you'd expect them to follow is somewhere along these lines:

Attempt to troubleshoot flaps first (best to avoid the problem altogether)
Remove excess fuel (either dump or burn)
Pick suitable airport considering runway length, altitude, and safety gear (e.g. EMAS)
Declare emergency and prepare airport (ready the fire trucks, etc)
Approach above no-flaps stall speed and touchdown as close to the start of the runway as possible
Engage brakes, spoilers, and thrust-reversers as appropriate
"Please please please stop..."
Write a book.

[*] "If you can walk away from a landing, it's a good landing. If you use the airplane the next day, it's an outstanding landing."

A minor nitpick: Remove the excess fuel (either dump or burn) after picking a suitable airport ;)

@dooburt as long as you're nitpicking, declare an emergency first, otherwise you've got to follow your original fight plan. The order isn't strict.

that was a given - hence the ;) on the end. Written in humour. A comprehensive list nonetheless. +1.

Any aircraft can land without those devices. I would say that the Gimli Glider is a nice example, with no power it could not extend its flaps/slats.
They are used, as @ratchetfreak notes in the comments, to reduce the touchdown speed and, as a consequence, the runway length needed to reach a stop or taxiing velocity.
To be noted, also, that a safe landing is mostly defined by the vertical velocity at tochdown, usually in the order of 1-3 feet per second. See for example this accident report where it states

mild touchdown rates [...] less than 5 feet per second

Since the vertical component is the relevant parameter for a safe landing, and given that without flaps/slats the forward velocity will be larger than usual, the aircraft will have to approach with a shallower angle than the usual 3°.
The absence of thrust reversers, as you might imagine, will only affect the braking process.

The Shuttle Landing Facility's 15,000 foot runway isn't always available... any info on the A380's landing distance without flaps/slats/reversers? Is it indeed feasible on "normal" runways at large airports?

@dvnrrs I edited the answer to include a famous example. I have no data for the A380, sadly.

Didn't the Gimli Glider get stopped by having its nose gear collapse?

@dvnrrs yes, but the touchdown went fine

@dvnrrs - the landing gear didn't collapse, it was never locked down properly in the first place

Another example (also a deadstick landing) is Air Transat flt 236, an A332 that landed with no flaps, no spoilers, and no reverse thrust, only slats and braking. They landed fast, braked hard, deflated most of the tires and stopped using most of the 11,000 ft runway. However their vertical speed on touchdown was high enough to cause the aircraft to bounce

I have never seen a recommendation to approach at a shallower angle with no flaps, and in our training they teach us to approach at the usual 3 degree angle.  You still flare in order to reduce the descent rate when doing a no-flap landing.

@JonStory: ...causing it to collapse as soon as it touched the runway.

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